(Updated) If you’ve ever bought anything off Amazon or looked at restaurant reviews on Yelp, you’re intimately familiar with the power of word of mouth. Marketers know it too, at least as far as its persuasive effect on the listener is concerned. But now a new study by a marketing professor in Canada backs it up a step and seeks to understand how word of mouth affects the attitudes of the teller.

The study was based on the idea that when people make an effort to explain their experiences, they end up understanding those experiences better themselves. A better understanding of your own experiences — negative or positive — in turn dampens the emotional hold they have on you. The author writes in the Journal of Consumer Research:

Understanding negative events, such as romantic breakups, job losses or disturbing video clips leads individuals to feel less intense negative emotions about these events and to recover from them more quickly. Similarly, understanding positive events, such as graduating from high school, leads individuals to feel less intense positive emotions about these events.

Likewise, when it comes to word of mouth, the difference lies in the explanation, the authors reason. Imagine, for instance, writing a restaurant review on Yelp. You might simply report that the service in a restaurant was fast. Or you might explain that the service in a restaurant was fast because the place was empty. The second review increases your understanding of the experience, thereby decreasing positive emotions like gratitude associated with it and, in turn, lowering your evaluation of the restaurant.

By the same token, if you explain that service was slow because one of the restaurant’s ovens was broken, it decreases negative emotions like anger and elevates your evaluation of the place.

There’s a twist to this phenomenon: it holds true for so-called “hedonic” experiences, those that have an emotional or sensory component, such as eating in a restaurant or watching a film, but not for “utilitarian” ones that revolve around functionality, like using a vacuum cleaner or a USB storage device. Sharing such non-emotional experiences through word of mouth tends to enhance, rather than dampen, your evaluations of them, the author says:

Explaining that a USB stick is liked because it stores all of one’s data should increase evaluations by confirming the product’s usefulness and functionality. Conversely, explaining that a USB stick is disliked because it stores only some of one’s data should decrease evaluations by confirming the product’s uselessness and lack of functionality.

In a series of experiments, Sarah G. Moore, an assistant professor of marketing at the Alberta School of Business, University of Alberta, reinforced these hypotheses. In one pair of tests, for example, she asked people to describe either a recent restaurant experience or a recent technology purchase. In both cases, people were asked to fill in the blanks of a story, “mad libs” style, including statements like “The best part of the whole experience was _____” or “The best part of the whole experience was _____, because _____.” The former was part of the non-explanation condition, while the latter obviously required the participant to explain.

People were asked to use the types of words they’d choose if they were writing real reviews on Yelp or Amazon. Afterward, participants were asked to evaluate the experiences they had just reviewed, using a 9-point scale, and indicate whether they planned to share them again through word of mouth. (A control group in each case was asked to imagine a recent restaurant experience or technology purchase, but didn’t fill out the review.)

Participants who explained their positive restaurant experiences ended up scoring those experiences lower, compared with people in the control and non-explanation groups, the study found. Similarly, those who explained their bad experiences gave them higher scores than people who didn’t explain. Either way, people who engaged in explanation were less likely to want to retell their experiences later.

“Explaining why a chocolate cupcake tasted so divine makes us love the cupcake a little less,” Moore noted in a statement, “while explaining why a movie was so horrible makes us hate the movie a little less.”

Among people who wrote about tech purchases, however, the opposite trend emerged. Those who explained positive experiences rated their purchases more highly than the other groups; those who explained negative ones evaluated them more harshly. In both cases, people were more likely to want to recommend or retell their experiences through word of mouth.

Moore suggests that companies should take these effects into account, when considering the marketing of their products. “To manage these issues, firms could provide vocabularies or story schemas to consumers via advertising or design online review sites to help customers express experiences in specific ways,” she writes.

Bearing that unsavory proposition in mind, it would seem that the study’s real takeaway, at least for the average consumer, is that word of mouth is subjective and that knowing the context tends to make every opinion a little clearer. So next time you’re on Amazon or getting a restaurant recommendation from a friend, remember to take the reviews with a grain of salt.